The development in the paper industry is towards increasingly high demands on paperboard products manufactured. This applies both to the demand on mechanical properties and also to the ability of the material to produce a good printing result. New regulations for recovery increase demands for use of recycled fibers to a greater extent. This implies that ever poor fibers shall be used to produce paperboard products with ever high demands for quality.
A vast number of methods and machines for manufacturing paperboard are described in the literature and have been used in practice with greater or lesser success. The following may be mentioned by way of example: EP-0 511 186 A1, WO 92/06242, U.S. Pat. No. 4,961,824, EP-0 511 185 A1, U.S. Pat. No. 5,074,964, EP-0 233 058 B1 and the article entitled "Headbox for High-Consistency Forming" in Paper Technology 31, No. 2:14-18(February 1990). Common to these methods and machines is that they cannot easily fulfil the requirements mentioned above, particularly in the case of manufacturing folding boxboard which is composed of a top layer, an underliner, a bulky core and a back layer, where it is particularly important for the core to have the best possible properties, such as formation, bulk and grammage profile, and for the underliner to have such uniformity that the top layer formed thereon will have the best possible printability.
The object of the invention is to provide an improved method of manufacturing paperboard and an improved board machine enabling the increasingly high demands placed on paperboard products to be met.